Thanks for reaching out regarding your concern with converting an estimate to an invoice, @emmavank. Your satisfaction is our top priority, and let's work together to resolve the disappearance of Quantity.

I've replicated the scenario and encountered no difficulties converting an estimate to an invoice, specifically in the quantity field. In your case, you might be experiencing some browser-related issues.

To rectify this, log into your QuickBooks Online account using an incognito window. You can also use other supported browsers to learn what browsers need for the best experience when using QuickBooks. You can use these shortcut keys to access a private window:

• Mozilla Firefox: CTRL + Shift + P
• Microsoft Edge: CTRL + Shift + N
• Google Chrome: CTRL + Shift + N
• Safari: Command + Shift + N

After signing in, please convert the estimate to an invoice again and see if the issue remains. If it works, go back to your regular browser and clear the cache. The system occasionally behaves strangely when the browser frequently accesses pages. It could be due to corrupted cache files in your browser.

I've added this article to learn how to record payments when you receive customer invoice payments: Record invoice payments in QuickBooks Online.

Keep me posted on how things are going by leaving a comment below, I'll be sure to circle back and offer the necessary help.